Github user JoshRosen commented on the pull request:
https://github.com/apache/spark/pull/2712#issuecomment-58761280
Actually, I don't think that this is a bug. Instead, I think that the
behavior that you're seeing could be an instance of
[SPARK-1018](https://issues.apache.org/jira/browse/SPARK-1018), where calling
`take()` or `collect()` on a non-transformed HadoopRDD returns the same element
several times because the same `Writable` object is re-used.
There's actually a note about this in the `sequenceFile()` Java/Scaladoc
(added by
https://github.com/apache/spark/commit/7101017803a70f3267381498594c0e8c604f932c):
```scala
/** Get an RDD for a Hadoop SequenceFile with given key and value types.
*
* '''Note:''' Because Hadoop's RecordReader class re-uses the same
Writable object for each
* record, directly caching the returned RDD will create many references
to the same object.
* If you plan to directly cache Hadoop writable objects, you should
first copy them using
* a `map` function.
* */
```
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